Simulation of Thermal and Flow Phenomena in Smooth and Internally Rifled Tubes

Original scientific paper https://doi.org/10.2298/TSCI19S4163G Development of the heat transfer surfaces on the tube inside makes it very difficult or even impossible to determine the heat transfer coefficient analytically. This paper presents the experimental determination of the coefficient in an internally rifled tube with spiral ribs. The tests are carried out on a laboratory stand constructed at the Institute of Thermal Power Engineering of the Cracow University of Technology. The tube under analysis has found application in a supercritical circulating fluidized bed boiler. The heat transfer coefficient local values are determined for the Reynolds numbers included in the range of ~6000 to ~50000 and for three ranges of the heating elements power. As the medium flows through internally rifled tubes with spiral ribs, the heat transfer process gets intensified compared to similar processes taking place in smooth tubes. Based on the obtained experimental data, a correlation is developed enabling determination of the dimensionless Chilton-Colburn j factor. The equation form is selected so that a comparison with existing results of tests performed on rifled tubes can be made. Comparing the Nusselt number values calculated based on the developed correlation with those obtained using other correlations described in the literature, it can be observed that the criterial number is about twice higher. The research results confirm the thesis that the element internal geometry has a substantial impact on the heat transfer process.

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“…3, and the characteristic quantities are listed in tab. 1 [23][24][25][26]. A 5-metre long tube was used for the experiments.…”

Section: Test Stand For Experimental Determination Of the Heat Transfmentioning

confidence: 99%

Experimental determination of the heat transfer coefficient in internally rifled tubes

Grądziel

Majewski²,

Majdak

2019

THERM SCI

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“…General principles of the model allowing determining fluid parameters are presented in [6]. In order to increase the accuracy of calculations, we assume that the waterwall tube has been divided into infinitesimal control volumes.…”

Section: Problem Analysismentioning

confidence: 99%

“…Decreasing the value of thermal stresses and faster stabilization of the heat exchange process can also be obtained by using spirally-rifled tubes in power boilers. The comparison of the heat transfer performance for smooth tubes and internally rifled tubes with significantly larger internal surface is shown in [4][5][6]. The authors of the articles presented in them the comparison of the heat transfer performance in both types of tubes and compared the obtained results of numerical simulations with experimental data.…”

Section: Introductionmentioning

confidence: 99%

Analysis of thermal flow in waterwall tubes of the combustion chamber depending on the fluid parameters

Majdak

Grądziel

2019

THERM SCI

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Original scientific paper https://doi.org/10.2298/TSCI19S4333MThe article presents the method of determining the temperature distribution in waterwall tubes of the combustion chamber. To simulate the operating conditions of waterwall tubes have been selected the model with distributed parameters, which is based on the solution of equations of the energy, mass and momentum conservation laws. The purpose of the calculations is determining the enthalpy, mass-flow and pressure of the working fluid flowing inside the tubes. The balance equations have been transformed into a form in which spatial derivatives are on the left, and the right side contains time derivatives. Then the time derivatives were replaced with backward difference quotients, and the obtained system of differential equations was solved by the Runge-Kutta method. The analysis takes into account the variability of fluid parameters depending on the mass-flow at the inlet of the tube and heat flux on the surface of the tube. The analysis of fluid parameters was carried out based on operating parameters occurring in one of the Polish supercritical power plants. Then it was compared with characteristics for systems operating at increased or reduced thermal flux on the walls of the furnace or systems operating at increased or reduced massflow of the working fluid at the inlet to the waterwall tube.

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“…The article presents an analysis of the temperature distribution in two neighbouring smooth waterwall tubes, which are mounted on the furnace wall of a supercritical steam boiler. Fluid parameters were determined in accordance with the assumptions presented in [3][4][5]. In order to increase the precision of calculations, were assumed that the waterwall tube has been divided into small control volumes.…”

Section: Problem Analysismentioning

confidence: 99%

Influence of thermal and flow conditions on the temperature distribution in the evaporator tubes

Majdak

2019

E3S Web Conf.

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The article presents the results of thermal and flow analysis of the working conditions of neighbouring waterwall tubes, loaded with heat streams of different values. The numerical model used for the analysis, allowing to calculate the temperature distribution of the tubes and the fluid flowing throughthem at each time step depending on the thermophysical parameters of the fluid and the material from which the tubes were made. By using the algorithm it is possible to precisely determine the temperaturedistribution for tubes, allowing to determine the places where the most divergent temperatures occur and in which thermal stresses of the highest value may occur. Analysis for several adjacent tubes willallow for the effect of temperature differences in the tubes to the temperature of the fin which is connecting them and to collect data that may be used for the determination of stress distribution in the tubes and fins.

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Simulation of Thermal and Flow Phenomena in Smooth and Internally Rifled Tubes

Cited by 9 publications

References 3 publications

Experimental determination of the heat transfer coefficient in internally rifled tubes

Experimental determination of the heat transfer coefficient in internally rifled tubes

Analysis of thermal flow in waterwall tubes of the combustion chamber depending on the fluid parameters

Influence of thermal and flow conditions on the temperature distribution in the evaporator tubes

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